Chapter 2 AP* Chemistry

ATOMS, MOLECULES & IONS

2.1 THE EARLY HISTORY OF CHEMISTRY

• 1,000 B.C.—processing of ores to produce metals for weapons and

ornaments; use of embalming fluids
• 400 B.C.—Greeks—proposed all matter was make up of 4 “elements” : fire,
earth, water and air
• Democritus—first to use the term atomos to describe the ultimate, smallest
particles of matter
• Next 2,000 years—alchemy—a pseudoscience where people thought they
could turn metals into gold. Some good chemistry came from their
The highest honor given
by the American
efforts—lots of mistakes were made!
Chemical Society. He • 16th century—Georg Bauer, German , refined the process of extracting
discovered oxygen. Ben metals from ores & Paracelsus, Swiss, used minerals for medicinal
Franklin got him applications
interested in electricity
• Robert Boyle, English—first “chemist” to perform quantitative
and he observed graphite
conducts an electric experiments of pressure versus volume. Developed a working definition for
current. Politics forced “elements”.
him out of England and • 17th & 18th Centuries—Georg Stahl, German—suggested “phlogiston”
he died in the US in 1804. flowed OUT of burning material. An object stopped burning in a closed
The back side, pictured
below was given to Linus container since the air was “saturated with phlogiston”
Pauling in 1984. Pauling • Joseph Priestley, English—discovered oxygen which was originally called
was the only person to “dephlogisticated air”
win Nobel Prizes in TWO
Different fields:
Chemistry and Peace.
2.2 FUNDAMENTAL CHEMICAL LAWS

late 18th Century—Combustion studied extensively

•
•
CO2, N2, H2 and O2 discovered
•
list of elements continued to grow
•
Antione Lavoisier, French—explained the true
nature of combustion—published the first
modern chemistry textbook AND stated the
Law of Conservation of Mass. The French
Revolution broke out the same year his text was
published. He once collected taxes for the
government and was executed with a guillotine as an enemy of the
people in 1794. He was the first to insist on quantitative
experimentation.

THE LAW OF CONSERVATION OF MASS:

Mass is neither created nor destroyed.Joseph Proust, French—stated the Law of Definite Proportions

*AP is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product.
© 2008 by René McCormick. All rights reserved.
 THE LAW OF DEFINITE PROPORTIONS:

A given compound always contains exactly the same proportions of elements by mass.

• 1808--John Dalton stated the Law of Definite proportions. He then went on

to develop the Atomic Theory of Matter.

THE LAW OF MULTIPLE PROPORTIONS:

When two elements combine to form a series of compounds, the ratios of the
masses of the second element that combine with 1 gram of the first element can
always be reduced to small whole numbers.

Dalton considered compounds of carbon and oxygen and found:

Mass of Oxygen that
combines with 1 gram of C
Compound I 1.33 g
Compound II 2.66 g

Therefore Compound I may be CO while Compound II may be CO2.

Exercise 2.1 Illustrating the Law of Multiple Proportions

The following data were collected for several compounds of nitrogen and oxygen:

Mass of Nitrogen That Combines With 1 g of Oxygen

Compound A 1.750 g
Compound B 0.8750 g
Compound C 0.4375 g

Show how these data illustrate the law of multiple proportions.

The ratios of the masses of nitrogen combining with 1g of oxygen in
each pair of compound should be small while numbers A = 1.750 = 2
B 0.875 1

B = 0.875 = 2
C 0.4375 1

A = 1.750 = 4
C 0.4375 1

Atoms, Molecules and Ions 2

2.3 DALTON’S ATOMIC THEORY

Dalton’s ATOMIC THEORY OF MATTER: (based on knowledge at that time):

1. All matter is made of atoms. These indivisible and indestructible objects are the ultimate
chemical particles.
2. All the atoms of a given element are identical, in both weight and chemical properties.
However, atoms of different elements have different weights and different chemical properties.
3. Compounds are formed by the combination of different atoms in the ratio of small whole
numbers.
4. A chemical reaction involves only the combination, separation, or rearrangement of atoms;
atoms are neither created nor destroyed in the course of ordinary chemical reactions.

**TWO MODIFICATIONS HAVE BEEN MADE TO DALTON' S THEORY

1. Subatomic particles were discovered.
2. Isotopes were discovered.

• 1809 Joseph Gay-Lussac, French—performed experiments [at constant temperature and

pressure] and measured volumes of gases that reacted with each other.

• 1811 Avogardro, Italian—proposed his hypothesis regarding Gay-Lussac’s work [and you
thought he was just famous for 6.02 x 1023] He was basically ignored, so 50 years of confusion
followed.

AVOGADRO’S HYPOTHESIS:

At the same temperature and pressure, equal volumes of different gases contain the same
number of particles.

Atoms, Molecules and Ions 3

2.4 EARLY EXPERIMENTS TO CHARATERIZE THE ATOM

Based on the work of Dalton, Gay-Lussac, Avogadro, & others, chemistry was beginning to make
sense [even if YOU disagree!] and the concept of the atom was clearly a good idea!

THE ELECTRON

• J.J. Thomson, English (1898-1903)—found that when high voltage was applied to an evacuated
tube, a “ray” he called a cathode ray [since it emanated from the (-) electrode or cathode when
YOU apply a voltage across it] was produced.
o The ray was produced at the (-) electrode
o Repelled by the (-) pole of an applied electric field, E
o He postulated the ray was a stream of NEGATIVE particles now called electrons, e-

o He then measured the deflection of beams of e- to determine the charge-to-mass ratio

e C
= − 1 .7 6 × 1 0 8
m g
o e is charge on electron in Coulombs, (C) and m is its mass.
o Thomson discovered that he could repeat this deflection and
calculation using electrodes of different metals ∴ all metals
contained electrons and ALL ATOMS contained electrons
o Furthermore, all atoms were neutral ∴ there must be some (+)
charge within the atom and the “plum pudding” model was
born. Lord Kelvin may have played a role in the development
of this model. [the British call every dessert pudding—we’d
call it raisin bread where the raisins were the electrons
randomly distributed throughout the + bread]

• 1909 Robert Millikan, American—University of

Chicago, sprayed charged oil drops into a chamber.
Next, he halted their fall due to gravity by
adjusting the voltage across 2 charged plates. Now
the voltage needed to halt the fall and the mass of
the oil drop can be used to calculate the charge on
the oil drop which is a whole number multiple of
the electron charge. Mass of e- = 9.11 × 10-31 kg.

Atoms, Molecules and Ions 4

RADIOACTIVITY

• Henri Becquerel, French—found out quite by accident [serendipity] that a piece of mineral
containing uranium could produce its image on a photographic plate in the absence of light. He
called this radioactivity and attributed it to a spontaneous emission of radiation by the uranium
in the mineral sample.
• THREE types of radioactive emission:
o alpha, α--equivalent to a helium nucleus; the largest particle radioactive particle emitted;
7300 times the mass of an electron. 24 He Since these are larger that the rest, early atomic
studies often involved them.
o beta, β--a high speed electron. −10 β OR −10 e
o gamma, γ--pure energy, no particles at all! Most penetrating, therefore, most dangerous.

THE NUCLEAR ATOM

• 1911 Ernest Rutherford, England—A pioneer in radioactive studies, he carried out experiments
to test Thomson’s plum pudding model.
o Directed α particles at a thin sheet of gold foil. He thought that if Thomson was correct,
then the massive α particles would blast through the thin foil like “cannonballs through
gauze”. [He actually had a pair of graduate students Geiger & Marsden do the first
rounds of experiments.] He expected the α particles to pass through with minor and
occasional deflections.

o The results were astounding [poor Geiger and Marsden first suffered Rutherford’s wrath
and were told to try again—this couldn’t be!].
ƒ Most of the α particles did pass straight through, BUT many were deflected at
LARGE angles and some even REFLECTED!
ƒ Rutherford stated that was like “shooting a howitzer at a piece of tissue paper
and having the shell reflected back”.
ƒ He knew the plumb pudding model could not be correct!
ƒ Those particles with large deflection angles had a “close encounter” with the
dense positive center of the atom
ƒ Those that were reflected had a “direct hit”
ƒ He conceived the nuclear atom; that with a dense (+) core or nucleus

Atoms, Molecules and Ions 5

 ƒ This center contains most of the mass of the atom while the remainder of the
atom is empty space!

2.5 THE MODERN VIEW OF ATOMIC STRUCTURE: AN INTRODUCTION

ELEMENTS
All matter composed of only one type of atom is an element. There are 92 naturally occurring, all
others are manmade.

ATOMS
atom--the smallest particle of an element that retains the chemical properties of that element.
• nucleus--contains the protons and the neutrons; the electrons are
located outside the nucleus. Diameter = 10-13 cm. The electrons
are located 10-8cm from the nucleus. A mass of nuclear material
the size of a pea would weigh 250 million tons! Very dense!
- proton--positive charge, responsible for the identity of the
element, defines atomic number
- neutron--no charge, same size & mass as a proton,
responsible for isotopes, alters atomic mass number
- electron--negative charge, same size as a proton or
neutron, BUT 1/2,000 the mass of a proton or neutron,
responsible for bonding, hence reactions and ionizations,
easily added or removed.
• atomic number(Z)--The number of p+ in an atom. All atoms of
Particle Mass Charge
the same element have the same number of p+.
- -31
e 9.11 × 10 1- • mass number(A)--The sum of the number of neutrons and p+
p +
1.67 × 10 -27
1+ for an atom. A different mass number does not mean a different
n0 1.67 × 10-27 None
element--just an isotope.

mass number →
atomic numbe r→
A
Z Χ ← element symbol

• actual mass is not an integral number! mass defect--causes this and is related to the
energy binding the particles of the nucleus together
Exercise 2.2 Writing the Symbols for Atoms
Write the symbol for the atom that has an atomic number of 9 and a mass number of 19. How many
electrons and how many neutrons does this atom have?

F; 9 electrons and 10 neutrons

Atoms, Molecules and Ions 6

ISOTOPES
• isotopes--atoms having the same atomic number (# of p+) but a different number of neutrons
• most elements have at least two stable
isotopes, there are very few with only
one stable isotope (Al, F, P)
• hydrogens isotopes are so important they
have special names:
- 0 neutrons ) hydrogen
- 1 neutron ) deuterium
- 2 neutrons ) tritium

2.6 MOLECULES AND IONS

Electrons are responsible for bonding and chemical reactivity

• Chemical bonds—forces that hold atoms together

• Covalenet bonds—atoms share electrons and make molecules [independent units]; H2, CO2,
H2O, NH3, O2, CH4 to name a few.
• molecule--smallest unit of a compound that retains the chem. characteristics of the compound;
characteristics of the constituent elements are lost.
• molecular formula--uses symbols and subscripts to represent the composition of the molecule.
(Strictest sense--covalently bonded)
• structural formula—bonds are shown by lines [representing shared e- pairs]; may NOT
indicate shape
H O H O
H H

• ions--formed when electrons are lost or gained in ordinary chem.

reactions; affect size of atom dramatically
• cations--(+) ions; often metals since metals lose electrons to
become + charged
• anions--(-) ions; often nonmetals since nonmetals gain electrons to
become - charged
• polyatomic ions--units of atoms behaving as one entity ) MEMORIZE formula and
charge!
• ionic solids—Electrostatic forces hold ions together. Strong ∴ ions held close together
∴ solids.

Atoms, Molecules and Ions 7

2.7 AN INTRODUCTION TO THE PERIODIC TABLE

• Atomic number = number of protons and is Current Name Original Name Symbol
written above each symbol Antimony Stibium Sb
• metals—malleable, ductile & have luster; Copper Cuprum Cu
most of the elements are metals—exist as Iron Ferrum Fe
cations in a “sea of electrons” which accounts Lead Plumbum Pb
Mercury Hydrargyrum Hg
for their excellent conductive properties; form Potassium Kalium K
oxides [tarnish] readily and form POSITIVE Silver Argentum Ag
ions [cations]. Why must some have such Sodium Natrium Na
goofy symbols? Tin Stannum Sn
Tungsten Wolfram W
• groups or families--vertical columns; have
similar physical and chemical properties (based on similar electron configurations!!)
• group A—Representative elements
• group B--transition elements; all metals; have numerous oxidation/valence states
• periods--horizonal rows; progress from metals to metalloids [either side of the black
“stair step” line that separates metals from nonmetals] to nonmetals
• MEMORIZE:
1. ALKALI METALS—1A
2. ALKALINE EARTH METALS—2A
3. HALOGENS—7A
4. NOBLE (RARE) GASSES—8A

Atoms, Molecules and Ions 8

2.8 NAMING SIMPLE COMPOUNDS

BINARY IONIC COMPOUNDS

Naming + ions: usually metals
• monatomic, metal, cation → simply the name of the metal from which it is
derived. Al3+ is the aluminum ion
• transition metals form more than one ion; Roman Numerals (in) follow the ion=s
name. Cu2+ is copper(II) (Yeah, the no space thing between the ion’s name and
(II) looks strange, but it is the correct way to do it.)
Mercury (I) is an exception ) it is Hg22+ ∴ two Hg+ associated together.
• NH4+ is ammonium
• NO ROMAN NUMERAL WHEN USING silver, cadmium and zinc. [Arrange
their SYMBOLS in alphabetical order—first one is 1+ and the other two are 2+]
Naming - ions: monatomic and polyatomic
• MONATOMIC--add the suffix -ide to the stem of the nonmetal's name.
Halogens are called the halides.
• POLYATOMIC--quite common; oxyanions are the PA's containing oxygen.
- hypo--”ate” least oxygen
- -ite--”ate” more oxygen than hypo-
- -ate--”ate” more oxygen than -ite
- hyper---ate--”ate” the most oxygen
NAMING IONIC COMPOUNDS: The + ion name is given first followed by the name of the
negative ion.

Atoms, Molecules and Ions 9

Exercise 2.3 Naming Type I Binary Compounds
Name each binary compound.
a. CsF b. A1C13 c. LiH

a. cesium fluoride
b. aluminum chloride
c. lithium hydride

Exercise 2.4 Naming Type II Binary Compounds

Give the systematic name of each of the following compounds.
a. CuC1 b. HgO c. Fe2O3 d. MnO2 e. PbC12

a. copper(I) chloride,
b. mercury(II) oxide.
c. iron(III) oxide.
d. manganese(IV) oxide.
e. lead(II) chloride.

TYPE II:

Involve a transition metal that needs a

roman numeral
+2
Mercury (I) is Hg2

Exceptions: these never need a

roman numeral even though
transition metals. MEMORIZE
Ag+, Cd2+, Zn2+

Atoms, Molecules and Ions 10

Exercise 2.5 Naming Binary Compounds
Give the systematic name of each of the following compounds.

a. CoBr2 b. CaC12 c. A12O3 d. CrC13

a. Cobalt(II) bromide
b. Calcium chloride
c. Aluminume oxide
d. Chromium(III) chloride

Exercise 2.6 Naming Compounds Containing Polyatomic Ions

Give the systematic name of each of the following compounds.

a. Na2SO4 b. KH2PO4 c. Fe(NO3)3 d. Mn(OH)2

e. Na2SO3 f. Na2CO3 g. NaHCO3 h. CsC1O4
i. NaOC1 j. Na2SeO4 k. KBrO3

a. Sodium sulfate
b. Potassium dihydrogen phosphate
c. Iron(III) nitrate
d. Manganese(II) hydroxide
e. Sodium sulfite
f. Sodium carbonate
g. Sodium hydrogen carbonate
h. Cesium perchlorate
i. Sodium hypochlorite
j. Sodium selenate
k. Potassium bromate

NAMING BINARY COVALENT COMPOUNDS : (covalently bonded)

• use prefixes!!! Don’t forget the –ide ending as well.

Exercise 2.7 Naming Type III Binary Compounds

Name each of the following compounds.

a. PC15 b. PC13 c. SF6 d. SO3 e. SO2 f. CO2

a. Phosphorus pentachloride
b. Phosphorus trichloride
c. Sulfur hexafluoride
d. Sulfur trioxide
e. Sulfur dioxide
f. Carbon dioxide

Atoms, Molecules and Ions 11

 ACIDS

• hydrogen, if present, is listed first

- naming acids ) -ide → hydro [negative ion root]ic ACID
-ate → -ic ACID
-ite → -ous ACID

Atoms, Molecules and Ions 12

 • PAINS IN THE GLUTEUS MAXIMUS: these lovely creatures have been around
longer than the naming system and no one wanted to adapt!!
- water
- ammonia
- hydrazine
- phosphine
- nitric oxide
- nitrous oxide (“laughing gas”)

Exercise 2.8 Naming Various Types of Compounds

Give the systematic name for each of the following compounds.

a. P4O10 b. Nb2O5 c. Li2O2 d. Ti(NO3)4

a. Tetraphosphorus decaoxide
b. Niobium(V) oxide
c. Lithium peroxide
d. Titanium(IV) nitrate

Exercise 2.9 Writing Compound Formulas from Names

Given the following systematic names, write the formula for each compound.

a. Vanadium(V) fluoride b. Dioxygen difluoride

c. Rubidium peroxide d. Gallium oxide

a. VF5
b. O2F2
c. Rb2O2
d. Ga2O3

Atoms, Molecules and Ions 13